Phytoplankton ecology of Sechelt Inlet, a fjord system on the British Columbia coast. II. Potentially harmful species

Many temperate phytoplankton species considered harmful occur in the Sechelt Inlet system, Britsh Columbia, Canada. Some of the harmful species (Chaetoceros concavicornis, Nitzschia (Pseudonitzschia) pungens, and Dinophysis fortii) were predictable spatially and/or temporally on an annual basis. Other species (Alexandrium catenella and Heterosigma carterae) exhibited greater inter-annual variability and are probably influenced by cyclical events (e.g. El Niño Southern Oscillation) longer than the period of this study. The ecology of C. concavicornis suggested a physiological adaptation to low light, enabling this diatom to live along the pycnocline in stratified water away from turbulence. Fall blooms of C. concavicornis appear to be a function of lower temperatures and decreasing light levels characteristic of the summer-autumn transition. N. pungens was found to occur regularly in summer and autumn; populations during the latter period were chiefly composed of f. pungens but f. multiseries, which has been linked to domoic acid production, also occurred. One large bloom of A. catenella occurred in late September 1989, which appeared to originate from outside the inlet complex. This PSP (paralytic shellfish poison)-producing dinoflagellate was advected into the system where it found conditions favourable to form an extensive bloom, with cell concentrations well in excess of those considered harmful (1000 cells l−1) down to 10 m throughout. This led to the highest toxicity ever recorded in British Columbia (31 000 μg per 100 g shellfish). Dinophysis, which produces okadaic acid, formed subsurface concentrations exceeding the reportedly harmful level of 200 cells l−1. D. acuminata was the predominant Dinophysis species and was often abundant at 10 to 15 m in summer near the region of tidal turbulence. In autumn there was a regular increase in the D. fortii population at 5 to 10 m in waters of the sheltered southern end. The fish killer H. carterae appeared as early as March in the relatively shallow waters of the southern end. The predominant pattern, however, was summer advection of H. carterae into the inlet complex from outside. Further stimulation of growth occurred at the confluence of 2 inlets where nutrient flux from tidal jets was possibly augmented by the chemical conditioning from waters overlying an anoxic bottom.